In setting threaded fasteners in mass production operations, power tools are customarily used to achieve both speed and accuracy in a final torque setting of a fastener to predetermined specifications. Hard-to-reach fasteners require tools with special reaching devices. One such conventional class of devices comprises a flat train of gears between a drive of a power tool and an output socket wherein the socket itself is a final gear of that train. Such a flat gear train device when utilized wth a power tool is called a crowfoot tool.
Ultimate torque capacity of such crowfoot tools is limited by the dimensions of the gear train device or output extension head which is necessary to reach a fastener. In this respect, the dimensions considered are the overall thickness of the head, the radius of the output end of that head and overall width of the head. When overloaded, stress on the gear teeth results in undesired damage. Such overloading commonly occurs when a desired fastener torque is relatively high and the width, thickness and radial dimensions referred to above are limited.
Torque capacity can be increased by increasing the thickness of the gear components alone (and thereby the thickness of the head), or by increasing the radial dimensions of the gear components and the head envelope width without increasing the head thickness. In practice, however, it is often imperative that the gear component thickness and radial dimensioning at the output socket gear end of the head remain constant due to dimensional constraints imposed by specific job applications.